DE102019215754A1 - Method of operating a current sensor and current sensor - Google Patents

Abstract

The invention relates to a method for operating a current sensor (10) which has a first measuring resistor (20), a second measuring resistor (22) and a reference resistor (36), the first measuring resistor (20) and the second measuring resistor (22) in series are arranged between a first connection (16) and a second connection (18) of the current sensor (10), and wherein the reference resistor (36) is electrically separated from the first measuring resistor (20) and the second measuring resistor (22) in a first measuring state, and the reference resistor (36) is electrically connected in parallel to the first measuring resistor (20) in a second measuring state, with the following steps: a) in the first measuring state determining the voltage drop across the first measuring resistor (20) and the voltage drop across the second measuring resistor (22) and determining the Ratio of the voltage drop across the first measuring resistor (20) and the voltage drop across the second measuring resistor (22), b) in the second measuring state, Ermitte In the voltage drop across the first measuring resistor (20), the voltage drop across the second measuring resistor (22) and the voltage drop across the reference resistor (36) and determining the electrical resistance of the first measuring resistor (20) and determining the electrical resistance of the second measuring resistor (22) from the determined voltage drops, the electrical resistance of the reference resistor (36) and the ratio of the voltage drops of the first measuring resistor (20) and the second measuring resistor (22) determined in the first measurement state. The invention also relates to a current sensor (10) for carrying out such a method.

Description

The invention relates to a method for operating a current sensor and a current sensor.

In many applications, especially in the vehicle sector, it is necessary to determine or measure the currents that occur very precisely. Methods and sensors are known from the prior art, for example, in which the current intensity is determined via the voltage drop across a measuring resistor arranged in the current path. For this it is necessary that the electrical resistance of the measuring resistor is known very precisely. In the vehicle sector, it is also necessary that the most exact measurement possible is ensured over the entire service life of the vehicle or the sensor, regardless of the temperature or external influences.

So far, therefore, special alloys have been used for the measuring resistor, for example a copper-nickel-manganese alloy, which has both a small change in electrical resistance over time and a low sensitivity to temperature changes.

However, these alloys are very expensive. Furthermore, the processing of these materials is very complex, since they have to be connected to the material of the rest of the current sensor.

In order to improve the accuracy of current sensors with measuring resistors, in particular with measuring resistors that have a greater temperature dependency or aging drift, current sensors are known from the prior art that are constantly recalibrated during operation. With these current sensors, the electrical resistance of the measuring resistor or a correction value for the electrical resistance of the measuring resistor is determined over the entire service life of the current sensor in order to compensate for changes in the electrical resistance of the measuring resistor caused by temperature or aging.

In a known method, a high-precision reference resistor is arranged parallel to the measuring resistor and part of the load current is briefly passed through the reference resistor. The voltage drop across the measuring resistor decreases according to the branched current pulse. The height of this current pulse is determined at the reference resistor. The electrical resistance of the measuring resistor or a correction value for the electrical resistance of the measuring resistor can be calculated from the ratio of the decrease in the voltage drop across the measuring resistor and the current pulse determined at the reference resistor.

In order to be able to precisely determine the electrical resistance of the measuring resistor, however, it is necessary that a load current that is as constant as possible is present at the time the electrical resistance is determined. If the load current changes before or while part of the load current is passed through the reference resistor, this can affect the accuracy of the determination of the current pulse through the reference resistor and thus the electrical resistance of the measuring resistor.

The object of the invention is to provide a method for operating a current sensor which enables the load current to be measured more precisely. Another object of the invention is to provide a current sensor which enables the load current to be determined more precisely.

1. a) im ersten Messzustand Ermitteln des Spannungsabfalls am ersten Messwiderstand und des Spannungsabfalls am zweiten Messwiderstand und Bestimmen des Verhältnisses des Spannungsabfalls am ersten Messwiderstand und des Spannungsabfalls am zweiten Messwiderstand,
2. b) im zweiten Messzustand Ermitteln des Spannungsabfalls am ersten Messwiderstand, Des Spannungsabfalls am zweiten Messwiderstand sowie des Spannungsabfalls am Referenzwiderstand und Bestimmen des elektrischen Widerstandes des ersten Messwiderstandes und Bestimmen des elektrischen Widerstandes des zweiten Messwiderstandes aus den ermittelten Spannungsabfällen, dem elektrischen Widerstand des Referenzwiderstandes und dem im ersten Messzustand bestimmten Verhältnis der Spannungsabfälle des ersten Messwiderstandes und des zweiten Messwiderstandes.

To achieve the object, a method for operating a current sensor is provided which has a first measuring resistor, a second measuring resistor and a reference resistor, the first measuring resistor and the second measuring resistor being arranged in series between a first connection and a second connection of the current sensor, and wherein the reference resistor is electrically separated from the first measuring resistor and from the second measuring resistor in a first measuring state and the reference resistor is connected electrically in parallel to the first measuring resistor in a second measuring state. The procedure consists of the following steps:

1. a) in the first measurement state, determining the voltage drop across the first measurement resistor and the voltage drop across the second measurement resistor and determining the ratio of the voltage drop across the first measurement resistor and the voltage drop across the second measurement resistor,
2. b) In the second measurement state, determining the voltage drop across the first measurement resistor, the voltage drop across the second measurement resistor and the voltage drop across the reference resistor and determining the electrical resistance of the first measurement resistor and determining the electrical resistance of the second measurement resistor from the voltage drops determined, the electrical resistance of the reference resistor and the in the first measuring state determined ratio of the voltage drops of the first measuring resistor and the second measuring resistor.

In step a), the ratio of the electrical resistances of the first and the second measuring resistor is first determined in the first measuring state. For this it is not necessary to adjust the electrical resistance of the first and / or the second To know the measuring resistor. Since the measuring resistors are arranged electrically in series, current fluctuations also have the same effect on the voltage drops across both measuring resistors, so that the ratio of the electrical resistances of the two measuring resistors can also be determined if current fluctuations occur.

In step b), the electrical resistance of the first measuring resistor is then determined in the second measuring state. In this measurement state, the reference resistor, the electrical resistance of which is known very precisely, is connected in parallel to the first resistor and the voltage drops across the first measurement resistor, the second measurement resistor and the reference resistor are measured. The voltage drop detected at the reference resistor and the known electrical resistance of the reference resistor can be used to determine the proportion of the current that flows through the reference resistor. The current flowing through the current sensor flows completely through the second measuring resistor and is divided between the current paths of the first measuring resistor and the reference resistor arranged parallel to this, which are arranged in series with the second measuring resistor. The current flowing through the second measuring resistor therefore corresponds to the added currents through the first measuring resistor and the reference resistor. The electrical resistance of the first measuring resistor can be calculated from the previously determined ratio of the electrical resistances of the first and second measuring resistors, the measured voltage drops at the first and second measuring resistors and the determined current via the reference resistor.

To determine the electrical resistance of the first measuring resistor, it is only necessary to determine the voltage drops at the measuring resistors and at the reference resistor. Furthermore, the electrical resistance of the reference resistor and the ratio of the electrical resistances of the first and the second measuring resistor must be known. It is not necessary to know the electrical resistance of the first or the second measuring resistor.

Any fluctuations in the load current that may exist during the second measurement state also occur on the second measurement resistor and can therefore be easily detected. These fluctuations can thus be taken into account when determining the electrical resistance of the first measuring resistor. Fluctuations in the load current can thus be taken into account when determining the electrical resistance of the first measuring resistor, so that the electrical resistance of the first measuring resistor can be determined more precisely.

• c) Im ersten Messzustand Ermitteln des Spannungsabfalls am ersten Messwiderstand und des Spannungsabfalls am zweiten Messwiderstand und Bestimmen des Verhältnisses des Spannungsabfalls am ersten Messwiderstand und des Spannungsabfalls am zweiten Messwiderstand und Bestimmen des elektrischen Widerstandes des zweiten Messwiderstandes aus den ermittelten Spannungsabfällen am ersten Messwiderstand und am zweiten Messwiderstand und dem in Schritt b) ermittelten elektrischen Widerstandes des zweiten Messwiderstandes.

After step b), the following step is preferably carried out:

• c) In the first measurement state, determining the voltage drop across the first measurement resistor and the voltage drop across the second measurement resistor and determining the ratio of the voltage drop across the first measurement resistor and the voltage drop across the second measurement resistor and determining the electrical resistance of the second measurement resistor from the determined voltage drops across the first measurement resistor and the second Measuring resistor and the electrical resistance of the second measuring resistor determined in step b).

If the electrical resistance of the first measuring resistor is known, the electrical resistance of the second measuring resistor can then be determined in a step c) in the first measuring state. For this purpose, the reference resistor is separated from the first measuring resistor in the second measuring state, so that no current flows through the reference resistor. The current thus flows completely through the first measuring resistor and the second measuring resistor arranged in series with it.

To determine the electrical resistance of the second measuring resistor, the voltage drop at the first measuring resistor is recorded and the amperage of the current is determined from the voltage drop and the known electrical resistance of the first measuring resistor or the one determined in the first measuring state. The voltage drop across the second measuring resistor is also determined. Since the series connection means that the current flowing through both measuring resistors must be the same, the current flowing through the second measuring resistor is known. The electrical resistance of the second measuring resistor can thus be determined from the current and the detected voltage drop.

Due to the series connection of the measuring resistors, current fluctuations affect the detection of the voltage drops for both measuring resistors. A change in current determined at the first measuring resistor can thus be taken into account when determining the electrical resistance of the second measuring resistor.

With the method described above, the electrical resistances of the measuring resistors can be determined very precisely regardless of current fluctuations. The only requirement is that the ratio of the electrical resistances of the first and the second determined in step a) Measuring resistor is known and does not change during the determination of the electrical resistances of the measuring resistors.

In addition, the current intensity of the current flowing through the current sensor is determined in both measurement states, so that an uninterrupted current measurement is ensured.

Steps b) and c) are preferably repeated alternately so that the two measuring resistors or the electrical resistances of the measuring resistors are constantly compared. In particular, through the alternating adjustment, the electrical resistances of the measuring resistor can be determined more precisely by iteration.

Before step a), the electrical resistance of the first measuring resistor can optionally be determined.

• - der über den ersten Messwiderstand fließende Strom aus dem Spannungsabfall am ersten Messwiderstand und dem elektrischen Widerstand des ersten Messwiderstandes bestimmt wird und/oder
• - der über den zweiten Messwiderstand fließende Strom aus dem Spannungsabfall am zweiten Messwiderstand und dem elektrischen Widerstand des zweiten Messwiderstandes bestimmt wird
• - und der über den Stromsensor fließende Laststrom aus dem über den ersten Messwiderstand fließenden Strom und/oder dem über den zweiten Messwiderstand fließenden Strom ermittelt wird.

The method can, for example, have the following steps in the first measurement state:

• the current flowing through the first measuring resistor is determined from the voltage drop across the first measuring resistor and the electrical resistance of the first measuring resistor and / or
• the current flowing through the second measuring resistor is determined from the voltage drop across the second measuring resistor and the electrical resistance of the second measuring resistor
• and the load current flowing via the current sensor is determined from the current flowing via the first measuring resistor and / or the current flowing via the second measuring resistor.

• - der über den ersten Messwiderstand fließende Strom aus dem Spannungsabfall am ersten Messwiderstand und dem elektrischen Widerstand des ersten Messwiderstandes bestimmt wird und/oder
• - der über den zweiten Messwiderstand fließende Strom aus dem Spannungsabfall am zweiten Messwiderstand und dem elektrischen Widerstand des zweiten Messwiderstandes bestimmt wird,
• - der über den Referenzwiderstand fließende Strom aus dem Spannungsabfall am Referenzwiderstand und dem elektrischen Widerstand des Referenzwiderstandes bestimmt wird
• - und der über den Stromsensor fließende Strom aus dem über den zweiten Messwiderstand fließenden Strom und/oder aus den addierten über den ersten Messwiderstand und den Referenzwiderstand fließenden Strömen ermittelt wird.

In the second measurement state, the method can have the following steps:

• the current flowing through the first measuring resistor is determined from the voltage drop across the first measuring resistor and the electrical resistance of the first measuring resistor and / or
• - the current flowing through the second measuring resistor is determined from the voltage drop across the second measuring resistor and the electrical resistance of the second measuring resistor,
• - The current flowing through the reference resistor is determined from the voltage drop across the reference resistor and the electrical resistance of the reference resistor
• and the current flowing via the current sensor is determined from the current flowing via the second measuring resistor and / or from the added currents flowing via the first measuring resistor and the reference resistor.

The voltage drops at the first measuring resistor, the second measuring resistor and the reference resistor are each recorded with a voltage detection device. The voltage drops are therefore recorded directly.

However, it is also possible to calculate individual voltage drops from measured voltage drops. For example, to determine the voltage drop at the second measuring resistor, the voltage drop at the first measuring resistor and the voltage drop at the first measuring resistor and at the second measuring resistor, i.e. the total voltage drop across the current sensor, can be detected and the voltage drop at the second measuring resistor can be determined from the difference between the detected voltage drops.

In addition, the voltage drop between the first connection and the second connection can be detected in the first and / or in the second measurement state. The voltage drop between the first connection and the second connection can be used to adjust the measured voltage drops across the first measuring resistor or the first measuring resistor and the reference resistor and the voltage drop across the second measuring resistor, so that the accuracy of the measurements, especially with small currents , can be improved.

To achieve the object, a current sensor for measuring a battery current, in particular a vehicle battery, is also provided, with a first measuring resistor, a second measuring resistor and a reference resistor. The first measuring resistor and the second measuring resistor are arranged in series between a first and a second connection of the current sensor. The reference resistor can be connected in parallel to the first measuring resistor. The current sensor also has a first voltage detection device for detecting the voltage drop across the first measuring resistor, a second voltage detection device for detecting the voltage drop across the second measuring resistor and a reference resistor voltage detection device for detecting the voltage drop across the reference resistor and an evaluation circuit for determining the electrical resistance of the first and second measuring resistors with a method described above.

It should be mentioned that the sequence of the measuring resistor in the current direction or between the connections can be varied as desired. It is only necessary that a first and a second measuring resistor are connected in series and a reference resistor can be connected temporarily in parallel to one of the measuring resistors or can be separated from them, and that the voltage drops across the resistors are each individually, for example with a voltage detection device can be captured.

A switching element is preferably provided which, in a closed position, establishes the parallel connection of the reference resistor to the first measuring resistor and, in an open position, separates the reference resistor from the first measuring resistor. With such a switching element, the reference resistor can easily be connected in parallel to or separated from the first measuring resistor.

The electrical resistances of the first measuring resistor and of the second measuring resistor are preferably essentially the same size.

Optionally, a third voltage detection device can be provided for detecting a voltage drop across the first measuring resistor and the second measuring resistor.

The measuring resistors can each be formed by a resistance element. However, it is also possible for the first measuring resistor and / or the second measuring resistor to have at least two measuring resistor elements arranged in series and / or in parallel.

• 1 eine erste Ausführungsform eines erfindungsgemäßen Stromsensors,
• 2 eine zweite Ausführungsform eines erfindungsgemäßen Stromsensors, und
• 3 eine dritte Ausführungsform eines erfindungsgemäßen Stromsensors.

Further advantages and features emerge from the following description in conjunction with the accompanying drawings. In these show

• 1 a first embodiment of a current sensor according to the invention,
• 2 a second embodiment of a current sensor according to the invention, and
• 3 a third embodiment of a current sensor according to the invention.

In 1 is a current sensor 10 to determine the load current 12th on a vehicle battery 14th shown. The current sensor 10 is used, for example, to determine the state of charge or the health of the vehicle battery 14th to determine.

The current sensor 10 has a first port 16 on, which can be contacted with the vehicle battery, and a second connection 18th , which is contacted, for example, on the vehicle body or a mass. The current sensor 10 is connected to the vehicle battery 14th connected that the entire load current through the current sensor 10 flows and can thus be detected by the current sensor.

The current sensor 10 has a first measuring resistor 20th and a second measuring resistor 22nd that are in series between the first connector 16 and the second port 18th are arranged. There are also two voltage detection devices 24 , 26th provided, each with a connection point 28 30th , 32 , 34 in front of and behind the measuring resistors 20th , 22nd are electrically contacted with these. The first voltage detector 24 can thus cause a voltage drop across the first measuring resistor 20th detect, the second voltage detection means 26th can cause a voltage drop across the second measuring resistor 22nd capture.

There is also a reference resistor 36 provided that has two connection points 38 , 40 parallel to the first measuring resistor 20th can be switched. The reference resistor 36 is a high-precision resistor made of a material that shows little or no change in electrical resistance due to temperature, external influences or aging.

At the reference resistor 36 is a switching element 42 provided to make the connection between the reference resistor 36 and the junction 40 to close or interrupt. Via the switching element 42 so can the reference resistance 36 parallel to the first measuring resistor 20th switched on or separated from them.

At the reference resistor 36 is also one about connection points 44 , 46 connected reference resistance voltage detection device 48 for detecting a voltage drop across the reference resistor 36 intended.

Flows through the current sensor 10 a load current 12th , are the voltage drops across the first and the second measuring resistor 20th , 22nd and from the recorded voltage drops and the electrical resistances of the measuring resistors 20th , 22nd the current strength of the current sensor via Ohm's law 10 flowing load current 12th certainly.

However, due to temperature changes, external influences or aging, the electrical resistance of the measuring resistors can change 20th , 22nd come. It is therefore necessary during the operation of the current sensor 10 the electrical resistances of the measuring resistors 20th , 22nd or correction factors for correction the electrical resistances of the measuring resistors 20th , 22nd to determine.

This is done using the method described in detail below.

First is the switching element 42 opened in a first switching state, so that the reference resistance 36 from the first measuring resistor 20th is separated. In this state, in the manner described above, the current sensor 10 flowing load current 12th to be determined. From the measured voltage drops across the measuring resistors 20th , 22nd can be the ratio of the electrical resistances R1, R2 of the first measuring resistor 20th and the second measuring resistor 22nd be calculated.

It applies $$\text{a}=\text{R1 / R2}=\text{U2 / U1}$$

The switching element is then in a second measurement state 42 closed so that the reference resistor 36 parallel to the first measuring resistor 20th is switched.

To determine the electrical resistance of the first measuring resistor 20th becomes with the second voltage detection device 26th the voltage drop across the second measuring resistor is recorded. Furthermore, at the same time as the first voltage detection device 24 the voltage drop across the first measuring resistor 20th detected. At the same time, the reference resistor voltage detection device 48 the voltage drop across the reference resistor 36 detected. From the recorded voltage drop across the reference resistor 36 and the known electrical resistance of the reference resistance, the current Iref des across the reference resistance 36 flowing current can be determined.

In the second measurement state, the entire load current flows 12th via the second measuring resistor 22nd . Due to the parallel connection of the first measuring resistor 20th and the reference resistance 36 the load current is divided between the two current paths via the first measuring resistor 20th and the reference resistance 36 on.

So the following applies: $$\text{I.}=\text{I.}2=\text{I.}1+\text{Iref}$$

und $$\text{a}\ast \text{U2/R1}=\text{U1/R1}+\text{Iref}$$

und $$\text{R}1=\left(\text{a}\ast \text{U2-U1}\right)\text{/Iref}$$

From 12 = U2 / R2 and a = U2 / U1 results $$\text{I.}=\text{U2 / R2}=\text{a}\ast \text{U2 / R1}$$

and $$\text{a}\ast \text{U2 / R1}=\text{U1 / R1}+\text{Iref}$$

and $$\text{R.}1=\left(\text{a}\ast \text{U2-U1}\right)\text{/ Iref}$$

It is therefore not necessary to measure the electrical resistance of the first or the second measuring resistor 20th , 22nd to know. All that is required is the previously determined ratio of the electrical resistances and the electrical resistance of the reference resistor 36 as well as the voltage drops across the measuring resistors 20th , 22nd as well as at the reference resistor 36 to eat.

Is the electrical resistance of the first measuring resistor 20th determined, the switching element is in the first measurement state 42 open, so the reference resistor 36 from the first measuring resistor 20th Cut. The load current therefore flows exclusively through the first measuring resistor 20th and the second measuring resistor 22nd .

Then the voltage detection device 24 the voltage drop across the first measuring resistor 20th detected and from the voltage drop and the previously determined electrical resistance of the first measuring resistor 20th the amperage of the load current 12th certainly

Furthermore, with the second voltage detection device 26th the voltage drop across the second measuring resistor 22nd detected. Since the measuring resistors 20th , 22nd are arranged in series, the amperage is correct via the second measuring resistor 22nd flowing current with the current strength of the first measuring resistor 20th flowing stream. From the recorded voltage drop across the second measuring resistor 22nd as well as from the voltage drop across the first measuring resistor 20th The electrical resistance of the second measuring resistor can thus be determined using Ohm's law 22nd to be determined.

The first measurement state and the second measurement state are preferably carried out alternately, so that the electrical resistances of the first measurement resistor are constantly compared 20th and the second measuring resistor 22nd he follows. In particular, due to the constant adjustment, the electrical resistances of the measuring resistors 20th , 22nd can be determined iteratively more precisely.

The advantage of the method described above is that the entire load current or its course is determined permanently, so that fluctuations in the load current when determining the electrical resistances of the measuring resistors 20th , 22nd can be taken into account.

Furthermore, the load current is always determined from the voltage drop across the first and / or the second measuring resistor 20th , 22nd . There is therefore an uninterrupted detection of the load current and, at the same time, a constant adjustment of the electrical resistances of the measuring resistors 20th , 22nd .

For the method described above, the position of the first measuring resistor is 20th to which the reference resistor 36 can be connected in parallel, irrelevant in the current direction. The first measuring resistor 20th can, as in 1 shown, be the rear measuring resistor with respect to the current direction S. The first measuring resistor 20th but can also, as in 2 shown, be the front measuring resistor in the current direction S.

The in 3 The current sensor shown differs from the one in 1 current sensor shown only by an additional voltage detection device 50 showing the voltage drop between the first terminal 16 and the second port 18th , i.e. the entire voltage drop across the current sensor.

This voltage drop can be used for comparison with the voltage drops described above or to improve the determination of the current strengths at the individual measuring resistors 20th , 22nd or the reference resistance 36 can be used, and thus for a more precise determination of the electrical resistances of the measuring resistors 20th , 22nd be used.

The electrical resistances are preferably the measuring resistors 20th , 22nd essentially the same size. However, these can also differ from one another.

The switching element 42 can be formed by any electrical components. Alternatively, the switching element 42 the connection to the port. 38 interrupt or close. There can also be two switching elements 42 be provided which is the reference resistor 36 completely disconnect from the current path.

The method described above is usually carried out by a controller in which the electrical resistances of the measuring resistors 20th , 22nd as well as the reference resistance 36 are stored and which controls the two measurement states described above.

List of reference symbols

10

Current sensor

12th

Load current

14th

Vehicle battery

16

first connection

18th

second connection

20th

first measuring resistor

22nd

second measuring resistor

24

first voltage detection means

26th

second voltage detection means

28

Junction

30th

Junction

32

Junction

34

Junction

36

Reference resistance

38

Junction

40

Junction

42

Switching element

44

Junction

46

Junction

48

Reference resistance voltage detection device

50

third voltage detection means

Claims (13)

Method for operating a current sensor (10) which has a first measuring resistor (20), a second measuring resistor (22) and a reference resistor (36), the first measuring resistor (20) and the second measuring resistor (22) in series between a first Terminal (16) and a second terminal (18) of the current sensor (10) are arranged, and wherein the reference resistor (36) in a first measuring state is electrically separated from the first measuring resistor (20) and from the second measuring resistor (22) and the reference resistor ( 36) is electrically connected in parallel to the first measuring resistor (20) in a second measuring state, with the following steps: a) In the first measuring state, determining the voltage drop across the first measuring resistor (20) and the voltage drop across the second measuring resistor (22) and determining the ratio of the voltage drop at the first measuring resistor (20) and the voltage drop at the second measuring resistor (22), b) in the second measuring state determining the voltage drop ls at the first measuring resistor (20), the voltage drop at the second measuring resistor (22) and the voltage drop across the reference resistor (36) and determining the electrical resistance of the first measuring resistor (20) and determining the electrical resistance of the second measuring resistor (22) from the determined voltage drops, the electrical resistance of the reference resistor (36) and the ratio determined in the first measurement state the voltage drops of the first measuring resistor (20) and the second measuring resistor (22). Procedure according to Claim 1 , characterized in that the following step is carried out after step b): c) In the first measurement state, determining the voltage drop across the first measurement resistor (20) and the voltage drop across the second measurement resistor (22) and determining the ratio of the voltage drop across the first measurement resistor (20) and the voltage drop at the second measuring resistor (22) and determining the electrical resistance of the second measuring resistor (20) from the determined voltage drops at the first measuring resistor (20) and at the second measuring resistor (22) and the electrical resistance of the second measuring resistor (22) determined in step b) ). Procedure according to Claim 2 , characterized in that steps b) and c) are repeated alternately. Method according to one of the preceding claims, characterized in that the electrical resistance of the first measuring resistor (20) is determined before step a). Method according to one of the preceding claims, characterized in that in the first measurement state - the current flowing across the first measurement resistor is determined from the voltage drop across the first measurement resistor (20) and the electrical resistance of the first measurement resistor and / or - the current flowing across the second measurement resistor Current is determined from the voltage drop across the second measuring resistor (22) and the electrical resistance of the second measuring resistor (22) - and the load current flowing through the current sensor is determined from the current flowing through the first measuring resistor and / or the current flowing through the second measuring resistor . Method according to one of the preceding claims, characterized in that in the second measuring state - the current flowing through the first measuring resistor is determined from the voltage drop across the first measuring resistor (20) and the electrical resistance of the first measuring resistor (20) and / or - the current flowing through the The current flowing through the second measuring resistor is determined from the voltage drop across the second measuring resistor (22) and the electrical resistance of the second measuring resistor (22), - the current flowing through the reference resistor from the voltage drop across the reference resistor (36) and the electrical resistance of the reference resistor (36) is determined - and the current flowing via the current sensor is determined from the current flowing via the second measuring resistor (22) and / or from the added currents flowing via the first measuring resistor (20) and the reference resistor (36). Method according to one of the preceding claims, characterized in that the voltage drops at the first measuring resistor (20), at the second measuring resistor (22) and at the reference resistor (36) are each detected with a voltage detection device (24, 26, 48). Method according to one of the preceding claims, characterized in that to determine the voltage drop across the second measurement resistor (22), the voltage drop across the first measurement resistor (20) and the voltage drop across the first measurement resistor (20) and the second measurement resistor (22) are recorded and the voltage drop across the second measuring resistor (22) is determined from the difference between the detected voltage drops. Current sensor (10) for measuring a battery current (12), in particular a vehicle battery (14), with a first measuring resistor (20), a second measuring resistor (22) and a reference resistor (36), the first measuring resistor (20) being the second measuring resistor (22) are arranged in series between a first connection (16) and a second connection (18) of the current sensor (10), and the reference resistor (36) in a first measuring state from the first measuring resistor (20) and the second measuring resistor (22 ) is electrically isolated and the reference resistor (36) is connected electrically in parallel to the first measuring resistor (20) in a second measuring state, with voltage detection devices (24, 26, 48, 50) for determining the voltage drops across the first measuring resistor (20) and the second measuring resistor (22) and on the reference resistor (36), and with a controller for determining the electrical resistance of the first measuring resistor (20) and the second measuring resistor (22) mi t a method according to any one of the preceding claims. Current sensor after Claim 9 , characterized in that a switching element (42) is provided that, in a closed position, connects the reference resistor (36) in parallel to the first measuring resistor (20). Current sensor according to one of the Claims 9 and 10 , characterized in that a first voltage detection device (24) is provided for detecting a voltage drop across the first measuring resistor (20) and / or a second voltage detecting device (26) is provided for detecting a voltage drop across the second measuring resistor (22), and that a reference current voltage detection device ( 48) is provided for detecting a voltage drop at the reference resistor (36). Current sensor according to one of the Claims 9 to 11 , characterized in that a third voltage detection device (50) is provided for detecting a voltage drop across the first measuring resistor (2) and the second measuring resistor (22). Current sensor according to one of the Claims 9 to 12th , characterized in that the electrical resistances of the first measuring resistor (20) and the second measuring resistor (22) are essentially the same size.

Images